class Compiler {
  constructor(vm) {
    this.el = vm.$el
    this.vm = vm
    this.compile(this.el)
  }

  // 编译模板 处理文本节点和元素节点
  compile(el) {
    let childNodes = el.childNodes
    Array.from(childNodes).forEach(node => {
      // 处理文本节点
      if (this.isTextNode(node)) {
        this.compileText(node)
      } else if (this.isElementNode(node)) {
        // 处理元素节点
        this.compileElement(node)
      }

      // 判断node节点 是否有子节点 如果有子节点 递归调用compile
      if (node.childNodes && node.childNodes.length) {
        this.compile(node)
      }
    })
  }

  // 编译元素节点 处理指令
  compileElement(node) {
    // console.log(node.attributes)
    // 遍历所有的属性节点
    Array.from(node.attributes).forEach(attr => {
      // 判断是否是指令
      let attrName = attr.name
      if (this.isDirective(attrName)) {
        // v-text => text
        attrName = attrName.substr(2)
        let key = attr.value
        this.update(node, key, attrName)
      }
    })
  } 

  update(node, key, attrName) {
    let updateFn = "";
    let index = attrName.lastIndexOf(":") 
    if (index !== -1) {
      updateFn = this[attrName.substring(0, index) + 'Updater']
    } else {
      updateFn = this[attrName + 'Updater']
    }
    updateFn && updateFn.call(this, node, this.vm[key], key, attrName.substring(index + 1))
  }
  // 处理 v-text
  textUpdater(node, value, key) {
    node.textContent = value
    new Watcher(this.vm, key, (newValue) => {
      node.textContent = newValue
    })
  }
  // v-module 
  moduleUpdater(node, value, key) {
    node.value = value
    new Watcher(this.vm, key, (newValue) => {
      node.value = newValue
    })
    // 双向绑定
    node.addEventListener('input', () => {
      this.vm[key] = node.value
    })
  }
  // v-html
  htmlUpdater(node, value, key) {
    node.innerHTML = value
    new Watcher(this.vm, key, (newValue) => {
      node.innerHTML = newValue
    })
  }
  // v-on:click
  onUpdater(node, value, key, eventName) {
    const fn = this.vm.$options.methods && this.vm.$options.methods[key]
    if (eventName && fn) {
      node.addEventListener(eventName, fn.bind(this.vm))
    }
  }

  // 编译文本节点 处理差值表达式
  compileText(node) {
    // console.dir(node);
    let reg = /\{\{(.+?)\}\}/
    let value = node.textContent
    if (reg.test(value)) {
      let key = RegExp.$1.trim()
      node.textContent = value.replace(reg, this.vm[key])

      // 创建watcher对象 当数据改变更新视图
      new Watcher(this.vm, key, (newValue) => {
        node.textContent = newValue
      })
    }
  }

  // 判断元素属性是否是指令
  isDirective(attrName) {
    return attrName.startsWith('v-')
  }

  // 判断节点是否是文本节点
  isTextNode(node) {
    return node.nodeType === 3
  }

  // 判断节点是否是元素节点
  isElementNode(node) {
    return node.nodeType === 1
  }
}